1. Field of the Invention
This invention relates to semiconductor devices, and particularly to a method for using a differential eFUSE (Electrically Programmable Fuse) sense without the use of a reference fuse(s).
2. Description of Background
Electrically Programmable Fuses (eFUSEs) are widely used to implement memory redundancy functionality in dynamic random access memory (DRAM), static random access memory (SRAM), and embedded memory devices. Passing a sufficient current through an eFUSE structure typically programs the eFUSE, such that its resistance is significantly altered from its initially fabricated state. In order to determine whether a particular fuse has been programmed or not, a sense circuit may be used to detect one of two possible “states” of the fuse. More specifically, the sense circuit holds one of two latched values therein, which is determined by a comparison between a voltage developed by the sense circuit across the fuse and a reference voltage generated within the sense circuit. The reference voltage is designed to be between a fuse voltage corresponding to the programmed state and a fuse voltage corresponding to an unprogrammed state. However, eFUSEs with small changes in resistivity between programmed and unprogrammed states are difficult to sense reliably with a single ended fuse latch.
Instead, a fuse sense device with higher gain and better discrimination is desirable to sense changes in resistance of a few hundred ohms. Conventional solutions have been proposed which use a first fuse, or resistive element as a reference device to which a fuse undergoing sensing is compared. This approach is operable but requires two fuses per bit, which reduces fuse bay density. Additionally, it is required to test for a fuse-blow margin and a conventional two fuse sensing system does not provide a means for margin testing. Two-element fuse sense systems have been proposed for the CMOS (Complementary Metal Oxide Semiconductor) technology but do not have margin test capabilities.
Considering the limitations of the above-mentioned methods, it is clear that there is a need for a method for detecting a state of an electronic fuse that does not utilize a two fuse sensing system.